<DIV>
<DIV>Dear Thomas,</DIV>
<DIV> </DIV>
<DIV>Thanks for your reply. I tried the neutral system before the charge one, which is simulated with Martyna-Tuckerman correction. The good thing is the band gap could achieve convergence in respect of super cell size. And I found that there is band gap between band 104 and 105 about 3.3 ev. But the occupation number of band 92-104 is fractional. The reason for that is there are lack of 4 electrons to occupy the band meanwhile I use smearing for the calculation. After adding 4 additional electrons to the system as I referred in the last email with the convergence size of supercell tested under neutral system (20 Angs), the band 92-104 are full occupation but decrease in band gap.</DIV>
<DIV> </DIV>
<DIV>So I thing the reason leads my problem may be relative to "curvature" in vacuum space, which you mentioned before. If it is, do you have any solution for that? Thank you.</DIV>
<DIV> </DIV>
<DIV>Best wishes</DIV>
<DIV>Yang</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>--------</DIV>
<DIV>
<P><FONT face=Calibri>Yang Zhou</FONT></P>
<P><FONT face=Calibri>PhD student</FONT></P>
<P><FONT face=Calibri>University of Leeds</FONT></P>
<P><FONT face=Calibri>United Kingdom</FONT></P></DIV></DIV>
<DIV>
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<DIV><B>From:</B> "Thomas Brumme"<thomas.brumme@uni-leipzig.de>;</DIV>
<DIV><B>Date:</B> Tue, Oct 22, 2019 10:37 PM</DIV>
<DIV><B>To:</B> "Quantum ESPRESSO users Forum"<users@lists.quantum-espresso.org>;"Leo Yang"<121076797@qq.com>;<WBR></DIV>
<DIV></DIV>
<DIV><B>Subject:</B> Re: [QE-users] band convergece problem in charged system</DIV></DIV>
<DIV><BR></DIV>Dear Yang,<BR><BR>I have no clue how the Martyna-Tuckerman correction works but usually one<BR>has problems with systems having such a large total charge since the total<BR>cell needs to be neutral. Some terms are in fact calculated for a charge neutral<BR>system resulting in a total potential which has a curvature as if there would be<BR>a homogeneous background charge. This constant curvature leads to a<BR>potential energy minimum in the vacuum space between the repeated cells.<BR>If you increase the cell this minimum goes down in energy and, at some point,<BR>crosses the Fermi energy and gets occupied.<BR><BR>Long story short:<BR>I have no clue but are you sure that Martyna-Tuckerman correction works<BR>correctly for charged systems?<BR>Is the LUMO really a state of the molecule and not from a state in the vacuum?<BR><BR>You could check if everything works as intended for a neutral system...<BR><BR>Regards<BR><BR>Thomas<BR><BR><BR>
<DIV class=moz-cite-prefix>On 10/2/19 1:46 PM, Leo Yang wrote:<BR></DIV>
<BLOCKQUOTE cite=mid:tencent_9AE1491B46369852087E7A69E6D083883108@qq.com type="cite">
<P>Dear QE users:</P>
<P>I try to use QE-6.4.1 to simulate <IMG id=x_x_x__x0000_i1025 style="CURSOR: pointer; HEIGHT: 18pt; WIDTH: 60.74pt" moz-do-not-send="true" originalsrc="cid:image002.png@01D55F54.3DEAB060" data-imagetype="AttachmentByCid" naturalwidth="81" naturalheight="24" data-custom="AAMkADYyNGE5ZDVlLWI0M2ItNGNkYi04NWUzLTgwMDBiYmY4MWE1YgBGAAAAAADT1egYenlfTqNtjOrIuhcjBwBEgTiP%2FR2ETam0o5puADWEAAAAAAEJAABEgTiP%2FR2ETam0o5puADWEAALgunFEAAABEgAQAIdmOwWosi9FpfzF8EHcwG8%3D" data-outlook-trace="F:3|T:3" crossorigin="use-credentials"><FONT face=Calibri> as single molecule. The system is built in large super cell, and <EM>total_charge=-4</EM> is added to input file leading to charged system. When I do the convergence test in term of the super cell size (20 Angs - 30 Angs ), the variation for total energy is small: -1038.6784 Ry for 20 Angs and 1038.7388 Ry for 30 Angs. But the band energy and Fermi energy (5.23 ev to 3.08 ev) shift visibly. The problem is that the band gap between band 104 (occupied) and 105 (unoccupied) become smaller with the increase of size (about 0.81 ev change to 0.11 ev). It seems the band gap is gradually disappear, which confuses me so much. The input file is attached with this email. It will be very appreciated if you can solve this for me. Thank you.</FONT></P>
<P><FONT face=Calibri><BR></FONT></P>
<P><FONT face=Calibri>Best wishes</FONT></P>
<P><FONT face=Calibri>Yang Zhou</FONT></P>
<P><FONT face=Calibri><BR></FONT></P>
<P><FONT face=Calibri>------</FONT></P>
<P><FONT face=Calibri>Yang Zhou</FONT></P>
<P><FONT face=Calibri>PhD student</FONT></P>
<P><FONT face=Calibri>University of Leeds</FONT></P>
<P><FONT face=Calibri>United Kingdom</FONT></P><BR>
<FIELDSET class=mimeAttachmentHeader></FIELDSET> <PRE class=moz-quote-pre wrap="">_______________________________________________
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Dr. rer. nat. Thomas Brumme
Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
Leipzig University
Phillipp-Rosenthal-Strasse 31
04103 Leipzig
Tel: +49 (0)341 97 36456
email: <A class=moz-txt-link-abbreviated href="mailto:thomas.brumme@uni-leipzig.de">thomas.brumme@uni-leipzig.de</A>
</PRE></DIV>